Ruud, who fended off two break points in the opening match, became the first player to break after a few backhanded shots from his opponent.

Although Alcaraz continued to struggle to find the court, he had the opportunity to equalize in the next game, only to see his forehand go out of the net cordon at the break point.

Two more chances followed, but Ruud defied the danger and his determination was rewarded when Alcaraz again put a forehand out of bounds for a double break.

Ruud served with an ace to love in the second set from Alcaraz, who made 18 unforced errors and hit less than 50% of her first serves in the opener.

However, the Spaniard was grounded in the second set and suffered a first break after losing just one point in his first three service games.

It looked like he was trying to tie the match but Ruud fought back – earning himself two backbreak points with a strike to the baseline, but he only needed one point as he hit a backhand shot from Alcaraz.

As Alcaraz’s level continued to drop, a renewed Ruud, who was just two points away from losing the set, broke again before serving out the win with an ace on the third match point, completing a streak of five consecutive matches.

Alcaraz and Ruud are joined in the John Newcombe Group by two-time ATP Finals champion Alexander Zverev of Germany and Russian Andrey Rublev, who plays from 19:30 GMT on Monday evening.